dparge, you are essentially correct. GRZ does own it's own studies and has control of them, and KRY owns theirs, but remember that some of the KRY work was done by Placer Dome and was made available to them by the CVG so the ownership of at least part of the data KRY is using is certainly in the possession of the CVG.
As to why RML would be better for VZ than KRY or GRZ. Technically, they wouldn't be but I suspect it is a political decision not a technical or economic one.
RML is also probably quite prepared to give away 50% of LB and LC to the government especially if it costs them nothing to get it. For the government to try to force a 50% ownership deal on KRY and GRZ now while there are valid contracts and agreements in place would void the existing agreements and cost them either as a settlement or legal compensation.